This invention relates to closures, and more particularly, to a process for making a composite plastic closure for bottles.
Various machines and processes have been developed over the years for lining metal crowns. For example, the Nagy machine shown in U.S. Pat. Nos. 1,931,294 and 2,069,987, and the Johnson machine shown in U.S. Pat. No. 1,852,578, were developed for lining metal crowns with cork liners. The process and machines shown in U.S. Pat. Nos. 1,486,937, 2,516,647, 2,548,305, 2,688,776, 2,719,564, 2,745,135, 2,877,493, 2,952,035 and 2,952,036, were developed for lining metal crowns with rubber liners. Subsequently, the Wilkens, Simpson and Aichele machines, and similar machines, shown in U.S. Pat. Nos. 2,684,774, 2,696,318, 2,840,858, 2,851,727, 2,881,475, 2,930,081, 2,954,585, 2,963,738, 3,029,765, 3,135,019, 3,577,595, 3,674,393, 3,827,843 and 3,877,497, were developed for lining metal crowns with thermosetting plastic or with thermoplastic. The above machines and processes have met with varying degrees of success.
Recently, the advantages of plastic crowns and closures have been recognized. The physical characteristics and nature of plastics, however, such as their melting and plastic deformation temperatures, and their resiliency, impact and compression strengths at molding and refrigeration temperatures present different structural problems in molding plastic closures than in forming metal closures.
In prior art plastic closures, for example, the wall thickness is confined to a limited range, i.e., the wall must be thin enough to permit axial removal and deflection of the threaded skirt of the closure from the plunger, but thick enough to support the necessary thread height and profile. The threads of conventional plastic closures are also limited to a certain amount of taper to permit deflection and removal of the threaded skirt from the plunger.
In conventional plastic closures, such as polypropylene closures, the closures often have low impact strength and fail a drop test in the refrigeration range of 32-40 degrees F.
It is therefore desirable to provide an improved process for making a composite plastic closure which overcomes most, if not all of the above disadvantages.